Device-to-device (D2D) channel management with network-assisted reference signal transmission

ABSTRACT

A base station (eNB) determines device-to-device (D2D) transmission parameters for signal transmission over a D2D communication link between a first user equipment (UE) device and a second UE device. The eNB instructs the first UE device to transmit a reference signal that is received by the second UE device. The second UE device reports D2D channel characteristic information indicative of the received reference signal. Based on the D2D channel characteristic information, the base station determines the D2D transmission parameters and provides the parameters to the first UE device.

CLAIM OF PRIORITY

The present application is a continuation of and claims priority to U.S.application Ser. No. 15/329,915, entitled “DEVICE-TO-DEVICE (D2D)CHANNEL MANAGEMENT WITH NETWORK-ASSISTED REFERENCE SIGNAL TRANSMISSION”and filed on Jan. 27, 2017, which is a national stage application ofPCT/US2015/044075, entitled “DEVICE-TO-DEVICE (D2D) CHANNEL MANAGEMENTWITH NETWORK-ASSISTED REFERENCE SIGNAL TRANSMISSION” and filed on Aug.6, 2015, which claims priority to Provisional Application No. 62/034,951entitled “Network-Assisted D2D Transmit UE Reference Signal” and filedAug. 8, 2014, all of which are assigned to the assignee hereof andhereby expressly incorporated by reference in their entirety.

FIELD

This invention generally relates to wireless communications and moreparticularly to device-to-device (D2D) channel management withnetwork-assisted reference signal transmission.

BACKGROUND

Many wireless communication systems use base stations to providegeographical service areas where wireless communication user equipment(UE) devices communicate with the base station (evolved Node B, eNB)providing the particular geographical service area in which the wirelesscommunication UE devices are located. The base stations are connectedwithin a network allowing communication links to be made between thewireless communication devices and other devices. In some situations,the communication links may be between UE devices within the servicearea of a base station. A cellular communication link between the UEdevices includes communication through the base station providing theservice. Where channel quality is sufficient, the UE devices cancommunicate directly through a device-to-device (D2D) communication linkthat does not include routing data through the base station. Somesituations, it may be preferred to have a direct D2D communication linkbetween the two UE devices rather than communicating through a basestation.

SUMMARY

A base station (eNB) determines device-to-device (D2D) transmissionparameters for signal transmission over a D2D communication link betweena first user equipment (UE) device and a second UE device. The eNBinstructs the first UE device to transmit a reference signal that isreceived by the second UE device. The second UE device reports D2Dchannel characteristic information indicative of the received referencesignal. Based on the D2D channel characteristic information, the basestation determines the D2D transmission parameters and provides theparameters to the first UE device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of cellular communication system thatsupports device-to-device (D2D) communication where a base station (eNB)determines D2D transmission parameters for D2D communication between afirst user equipment (UE) device and a second UE device based on D2Dchannel characteristic information determined from a reference signalreceived at the second UE device.

FIG. 1B is a block diagram of the communication system where the eNBinstructs the first UE device to transmit a reference signal and thesecond UE device reports D2D channel characteristic information based onthe received reference signal.

FIG. 1C is a block diagram of the communication system where the eNBinstructs the first UE device and a third UE device to transmitreference signals at the same time and frequency to determine a level ofinterference.

FIG. 1D is a block diagram of the communication system where the eNBinstructs the first UE device and a third UE device to transmitreference signals at the same time and frequency to determine a level ofinterference with other D2D devices.

FIG. 2 is a block diagram of an example of a UE device suitable for useas one of the UE devices.

FIG. 3 is a block diagram of an example of a base station (eNB) suitablefor use as the base station (eNB) in FIG. 1.

FIG. 4 is a message diagram for an example of determining D2Dtransmission parameters based on network-assigned reference signaltransmissions.

FIG. 5 is a message diagram for an example of determining a level ofinterference at the eNB 108 based on network-assigned reference signaltransmissions.

FIG. 6 is a message diagram for an example of determining a level ofinterference at D2D UE devices based on network-assigned referencesignal transmissions.

FIG. 7 is a flowchart of an example of a method of managingcommunication using network-assisted reference signal transmissionperformed at an eNB.

FIG. 8 is an illustration of an example of a transmission by a D2D UEdevice including reference signals.

DETAILED DESCRIPTION

FIG. 1A is a block diagram of cellular communication system 100 thatsupports device-to-device (D2D) communication where a base station (eNB)determines D2D transmission parameters for D2D communication between afirst user equipment (UE) device 102 and a second UE device 104 based onD2D channel characteristic information determined from a referencesignal received at the second UE device. For the example, each of thetwo UE devices 102, 104 a can be a transmitting device and a receivingdevice although in some situations, a device may only be a receiving ortransmitting device. For the example of FIG. 1A and FIG. 1B, the firstUE device 102 and the second UE device 104 are within the geographicservice area 106 provided by a base station (eNB) 108 and are capable ofcommunicating over a D2D link. Even when the channel conditions may beadequate for supporting D2D communication, D2D may not be the preferredlink. A D2D communication link 110, as well as a cellular communicationlink 112, can be established for transmission of data between the firstUE device 102 and the second UE device 104. The D2D communication link110 is a direct wireless communication link between the first UE device102 and the second UE device 104 that does not route data through thebase station (eNB) 108. The cellular communication link 112 includes atleast a first portion 116 from the first UE device 102 to the basestation (eNB) 108 and a second portion 118 from the base station (eNB)108 to the second UE device 104. Therefore, sending data from the firstUE device 102 to the second UE device 104 includes an uplinktransmission to the eNB and a downlink transmission from the eNB to thesecond UE device. Uplink transmissions are transmitted in the firstportion 116 over one or more uplink channels 124. The base station 108transmits the downlink transmissions to the second UE device 102 overone or more downlink channels 126. The base station 108 can alsotransmit downlink signals to the first UE device 102 over downlinkchannels 128 and receive uplink signals from the second UE device overuplink channels 130. Accordingly, for the example, the cellularcommunication link is bidirectional.

Sending the data from the first UE device 102 to the second UE device104 over the D2D communication link 110 includes a D2D transmission 132over one or more D2D transmission channels 134. The first UE device canalso receive signals from the second UE device 104 over D2D receptionchannels 136. One or more of the D2D transmission channels 134 can bethe same as the D2D reception channels 136. For the examples herein, theD2D channels 134, 136 are a subset of cellular uplink channels. In somecases, downlink channels can be used.

The base station (eNB) 108 provides wireless communication services towireless communication user equipment (UE) devices 102, 104 within thegeographical service area 106, sometimes referred to as a cell. Severalbase stations are typically interconnected through a backhaul (notshown) to provide several service areas to cover large areas. Othersystem components forming system entities and performing systemfunctions such as Mobility Management Entity (MME), scheduling, gatewayand other functions are omitted from FIG. 1 in the interest of brevityand clarity. Any description with reference FIG. 1 of the variousfunctions and operations of such equipment may be implemented in anynumber of devices, circuits, or elements. Two or more functional blocksmay be integrated in a single device, and the functions described asperformed in any single device may be implemented over several devicesin some circumstances. A cellular communication system is typicallyrequired to adhere to a communication standard or specification. TheThird-Generation Partnership Project Long-Term Evolution (3GPP LTE)communication specification is a specification for systems where basestations (eNodeBs) provide service to wireless communication devices(user equipment (UE) devices) using orthogonal frequency-divisionmultiplexing (OFDM) on the downlink and single-carrierfrequency-division multiple access (SC-FDMA) on the uplink. Although thetechniques described herein may be applied in other types ofcommunication systems, the exemplary systems discussed herein operate inaccordance with at least one revision of the 3GPP LTE communicationspecification.

The base station (eNB) 108 is a fixed transceiver station, sometimesreferred to as an evolved Node B, eNodeB or eNB, which may include acontroller in some circumstances. The base station 108 may be connectedto a controller through a backhaul which may include any combination ofwired, optical, and/or wireless communication channels. The controllermay include the functionality of the Mobility Management Entity (MME)and the Packet Gateway (P-GW) in a 3GPP LTE communication system.

The wireless (UE) communication devices (UE devices) 102, 104 may bereferred to as mobile devices, wireless devices, wireless communicationdevices, mobile wireless devices, user equipment, UEs, UE devices aswell as by other terms. The UE devices 102, 104 include electronics andcode for communicating with base stations and with other wirelesscommunication devices in D2D configurations. The UE devices may includedevices such as cell phones, personal digital assistants (PDAs),wireless modem cards, wireless modems, televisions with wirelesscommunication electronics, and laptop and desktop computers as well asother devices. The combination of wireless communication electronicswith an electronic device, therefore, may form a UE device 102, 104. Forexample, a UE device may include a wireless modem connected to anappliance, computer, or television.

The base station 108 includes a wireless transceiver that exchangeswireless signals with the UE devices 102, 104. Transmissions from thebase stations and from the UE devices 102, 104 are governed by acommunication specification that defines signaling, protocols, andparameters of the transmission. The communication specification mayprovide strict rules for communication and may also provide generalrequirements where specific implementations may vary while stilladhering to the communication specification. Although the discussionbelow is directed to the 3GPP Long Term Evolution (LTE) communicationspecification, other communication specifications may be used in somecircumstances. The communication specification defines at least a datachannel and a control channel for uplink and downlink transmissions andspecifies at least some timing and frequency parameters for physicaldownlink control channels from a base station to a UE device.

As discussed below in further detail, the eNB 108 instructs the first UEdevice 102 to transmit a reference signal. The first UE device transmitsthe reference signal 140 which is received by the second UE device 104.Based on the received reference signal, the second UE device 104determines and transmits D2D channel characteristics information 142 tothe eNB 108. Based on the D2D channel characteristics information 142,the eNB determines the D2D transmission parameters that should be usedby the first UE device 102 for D2D transmission 132 to the second UEdevice 104.

FIG. 1B is a block diagram of the communication system 100 where the eNB108 instructs the first UE device 102 to transmit a reference signal 140and the second UE device reports D2D channel characteristic information142 based on the received reference signal. The eNB 108 sends areference signal transmission instruction 144 to the first UE device 102instructing the UE device to transmit a reference signal 140. Theinstruction 144 identifies the communication resources that should beused by the first UE device 102 to transmit the reference signal 140.For the example, the instruction 144 is transmitted on a downlinkchannel such as the PDCCH/PDSCH or higher layer signaling. In somesituations, the reference signal transmission instruction 144 can bebroadcast over a System Information Block (SIB). Such as technique maybe useful when a set of D2D UE devices are instructed at the same time.Other channels can be used to transmit the reference signal transmissioninstruction 144.

The reference signal transmission instruction 144 specificallyidentifies the resources that the UE device should use for transmittingthe reference signal in some situations. In other situations, thereference signal transmission instruction 144 can identify a set ofresources that the UE device may use for reference signal transmissionand the UE device is instructed to autonomously select communicationresources from the set to transmit a reference signal when the UE deviceis interested in D2D communication. For the examples, the referencesignal transmission instruction 144 identifies the frequency/timecommunication resources for reference signal transmission and the powerlevel for transmitting the reference signal. The power level may bebased on the closed loop power control between the eNB and the first UEdevice. A fixed known transmission power level known to the eNB is usedfor the reference signal. In one example, the eNB can provide thisparameter in the SIB messaging to all the UE devices. In anotherexample, the eNB can indicate the transmission power level to the firstUE device based on the received uplink power level.

The reference signal 140 is transmitted on the carrier that will be usedfor D2D communication. For the example, therefore, the reference signal140 is transmitted on the uplink carrier that is allocated for D2Dcommunication.

As discussed below with reference to FIG. 1C, the reference signal 140may be received by the eNB in some situations. As discussed below, theeNB can instructs multiple UE devices to transmit the reference signalat the same frequency and time to determine the level of interferencedue to other UE devices. Such a technique is optional and may not beperformed every time the D2D channel characteristic is reported,however. As a result, a dashed line represents the reference signalreceived by the eNB 108 in FIG. 1B.

The eNB 108 also transmits a reference signal reception instruction 146to the second UE device 104 (target UE device) where the instruction 146indicates the communication resources that will be used to transmit thereference signal 140 from the first UE device. For the example, theinstruction 144 is transmitted in a downlink channel such as thePDCCH/PDSCH and/or higher layer signaling. Other channels can be used.In some situations, the reference signal reception instruction 146identifies the set of resources that may be used for reference signaltransmission. For example, the reference signal reception instruction146 can be sent via SIB messaging. Therefore, the second UE device mayreport the D2D channel characteristics when the first UE deviceautonomously selects communication resources and transmits a referencesignal that is received by the second UE device. The instruction 146also identifies communication resources that should be used by thesecond UE device to transmit D2D channel characteristic information tothe eNB 108. In some situations, the communication resources forreporting the channel information may be provided by the eNB in aseparate message. The second UE device 104 receives the reference signal140 and determines the D2D channel characteristic information that isthen reported to the eNB 108.

The D2D channel characteristic information 142 determined by the secondUE device 104 may include various types of information and formats. Thesecond UE device 104 measures, or otherwise evaluates, the referencesignal 140 transmitted from the transmitting UE device over the D2Dtransmission channel 134. For the example, the technique for measuringevaluating the reference signal (D2D transmission channel) is similar toconventional techniques used in 3GPP LTE systems for determining uplinkchannel state information (CSI) by eNBs for the uplink channels. Theactual D2D CSI parameters may be sent to the eNB 108 as the D2D channelcharacteristic information 142. In some situations, however, the D2Dchannel characteristic information 142 sent to the eNB 108 may beinformation based on the CSI parameters. For example, the informationmay be derived from the CSI parameters and not the actual CSIparameters. For the example, therefore, the D2D channel characteristicinformation 142 is at least indicative of the CSI parameters measured bythe second UE device. Although the second UE device may report the D2Dchannel characteristic information after receiving a single referencesignal, the UE device reports information based on multiple referencesignals received over time in the example. For the example, therefore,multiple reference signals are received and processed to determine theCSI parameters. Techniques such as time averaging and filtering can beused to process the measurements and generate the CSI reports.

FIG. 1C is a block diagram of the communication system 100 where the eNB108 instructs the first UE device 102 and a third UE device 148 totransmit reference signals 140, 150 at the same time and frequency todetermine a level of interference. For the example in FIG. 1C, the thirdUE device 148 is a cellular UE device that is, or will be, communicatingusing cellular communication links and not D2D communication links. TheeNB 108 instructs the third UE device 148 to transmit the referencesignal 150 by sending a reference signal transmission instruction 152 tothe third UE device 148. The instruction 152 provides reference signaltransmission parameters that result in transmission of the reference 150signal at the same time and frequency as the reference signal 140transmitted from the first UE device. Under certain conditions, thereference signal 140 will cause interference with the reference signal150. The eNB receives both reference signals 140, 150 and determines ifthe level of interference is tolerable (e.g., below a threshold). TheeNB takes into account the interference level when determining the D2Dtransmission parameters. For example, if the interference cannot betolerated, the time/frequency communication resources are not reused. Inother words, the same communication resources are not assigned todifferent UE devices where interference of their reference signals isabove a threshold.

FIG. 1D is a block diagram of the communication system 100 where the eNB108 instructs the first UE device 102 and a third UE device 154 totransmit reference signals 140, 156 at the same time and frequency todetermine a level of interference with other D2D devices. When multiplepairs of D2D UE devices are communicating in proximity to each other, itis possible that their transmissions will cause interference when thesame communication resources are being used. On the other hand, theobjective to efficiently use communication resources requires that thecommunication be reused when possible. For the example of FIG. 1D,reference signal are used to determine whether communication resourcescan be reused for D2D communication between different sets of D2D UEdevices. For the example of FIG. 1D, the third UE device 154 is a D2D UEdevice that is using, or has requested to use, D2D communicationresources. The eNB 108 instructs the third UE device 154 to transmit thereference signal 156 by sending a reference signal transmissioninstruction 158 to the third UE device 154. The instruction 158 providesreference signal transmission parameters that result in transmission ofthe reference 156 signal at the same time and frequency as the referencesignal 140 transmitted from the first UE device. Under certainconditions, the reference signal 140 will cause interference with thereference signal 156 at other UE devices and/or the reference signal 156will cause interference with the reference signal 140. The eNB sends areference signal reception instruction 160 to a fourth UE device 162inform the fourth UE device of the transmission of the reference signal156 and to provide information to assist the UE device in receiving thereference signal 156. The second UE device 104 determines the level ofinterference caused by the second reference signal 156 to the firstreference signal 140 and reports the interference to the eNB. The fourthUE device 162 determines the level of interference caused by the firstreference signal 140 to the second reference signal 156 and reports theinterference to the eNB. The interference information that is reportedmay include any type of parameters that indicate the level ofinterference. Examples of suitable interference parameters include thepower levels of the reference signals and power ratios of the powerlevels such as signal to-noise-ratio (SNR),signal-to-interference-plus-noise ratio (SINR) (also known as thesignal-to-noise-plus-interference ratio (SNIR)) or combinations thereof.The interference information may be reported as part of the D2D channelcharacteristic information 164 from the 4^(th) UE device or may betransmitted separately. The interference information determined by thesecond UE device may be transmitted in the D2D channel characteristicinformation 142.

Based on the interference information, the eNB determines whether thesame communication resources can be assigned to different sets of D2D UEdevices. If the interference is below a threshold, the eNB reuses thecommunication resources.

FIG. 2 is a block diagram of an example of a UE device 200 suitable foruse as one of the UE devices 102, 104, 148, 154, 162. The UE device 200includes a transceiver 202 and a controller 204, as well as othercomponents and circuitry (not shown) such as memory and a userinterface, for example.

The transceiver 202 includes a transmitter that transmits uplinkwireless signals to base stations (eNBs) and a receiver that receivesdownlink wireless signals from base stations (eNBs) over the uplink anddownlink channels, respectively. The transceiver 202 is also configuredto transmit and receive D2D signals using allocated cellular resources,such as uplink communication resources, for example. The controller 204controls components of the UE device 200 to manage the functions of thedevice 200 described herein as well as to facilitate the overallfunctionality of the device 200. The controller 204 is connected to thetransceiver 202 and other components such as memory.

The receiver in the transceiver 202 may also be used to measureparameters to determine channel characteristics for the downlink channeland the D2D channels. The controller and the receiver measure one ormore parameters that indicate channel characteristic information such asthe quality of the channel, required transmission power for transmissionthrough the channel, or power levels related to the received referencesignal such as total received power, signal to-noise-ratio (SNR),signal-to-interference-plus-noise ratio (SINR) (also known as thesignal-to-noise-plus-interference ratio (SNIR)) or combinations thereof.The controller 204 in the UE device 200 determines the CSI parametersbased on the measured channel parameters and generates CSI reports thatare sent to the eNB.

FIG. 3 is a block diagram of an example of a base station (eNB) 300suitable for use as the base station (eNB) 108 in FIG. 1. The basestation (eNB) 300 includes a transceiver 302, a controller 304, and acommunication interface 306 as well as other components and circuitry(not shown) such as memory, for example.

The transceiver 302 exchanges wireless signals with the UE devices 104,106 within the service area 106. Transmissions from the base station(eNB) and from the UE devices are governed by a communicationspecification that defines signaling, protocols, and parameters of thetransmission. The communication specification may provide strict rulesfor communication and may also provide general requirements wherespecific implementations may vary while still adhering to thecommunication specification. Although the discussion herein is directedto the 3GPP Long Term Evolution (LTE) communication specification, othercommunication specifications may be used in some circumstances. Thecommunication specification defines at least a data channel and acontrol channel for uplink and downlink transmissions and specifies atleast some timing and frequency parameters for physical channels.

The transceiver 302, therefore, includes at least a downlink transmitterfor transmitting downlink signals and an uplink receiver for receivinguplink signals. The receiver and controller measure one or moreparameters to determine characteristics of the uplink channels. Thereceiver, therefore, is capable of measuring the reference signaltransmitted by the UE devices to determines cellular channelcharacteristic information such as the quality of the cellular channel,required transmission power for transmission through the channel, and/orpower levels related to the received reference signal such as totalreceived power, signal to-noise-ratio (SNR),signal-to-interference-plus-noise ratio (SINR) (also known as thesignal-to-noise-plus-interference ratio (SNIR)) or combinations thereof.

For the example, the base station (eNB) 300 also includes acommunication interface 306 for facilitating communication over thebackhaul with other eNBs and network entities. Where X2 signaling isavailable, the communication interface 312 communicates over thebackhaul using X2.

In addition to other functions, the controller evaluates the channelcharacteristic information to allocate and assign communicationresources to UE devices including D2D UE devices and cellular UEdevices. The examples discussed with reference to FIG. 1A, FIG. 1B, FIG.1C and FIG. 1D may be performed independently or collectively. Forexample, the eNB may determine only D2D transmission parameters for aset of D2D UE devices in one situation. In other situations, the eNB maydetermine the D2D transmission parameters for multiple sets of D2D UEdevices and allocate communication resources for D2D and cellularcommunication.

FIG. 4 is a message diagram 400 for an example of determining D2Dtransmission parameters based on network-assigned reference signaltransmissions. The message transmission discussed with reference to FIG.4, therefore, provide an example of message transmission suitable forthe examples discussed with reference to FIG. 1A and FIG. 1B.

At transmission 402, the eNB 108 transmits a reference signaltransmission instruction 144 to the first UE device where theinstruction identifies the communication resources that should be usedby the first UE device to transmit a reference signal 140. For theexample, the instruction 144 is transmitted in the PDCCH/PDSCH althoughother channels can be used.

At transmission 404, the eNB 108 transmits a reference signal receptioninstruction 146 to the second UE device where the instruction 146identifies the communication resources that will be used by the first UEdevice to transmit the reference signal 140. For the example, theinstruction 146 is transmitted in the PDCCH/PDSCH although otherchannels can be used. In some situations, the reference signal receptioninstruction 146 identifies communication resources that should be usedby the second UE device to report the D2D channel characteristics to theeNB.

The first reference signal is transmitted by the first UE device 102 andreceived by the second UE device at transmission 406.

At event 408, the second UE device 104 determines the D2D channelcharacteristics D2D communication link 110. For the example, the secondUE device 104 received and evaluates toe reference signal to determineCSI parameters.

At transmission 410, the second UE device sends the D2D channelcharacteristic information to the eNB 108. For the example, the secondUE device 104 sends a message indicative of the CSI parameters over thecommunication resources identified by the eNB 108. Such communicationresources may include resources in the PUCCH/PUSCH, for example.

At event 412, the eNB determines the D2D transmission parameters fortransmitting D2D signals from the first UE device 102 to the second UEdevice 104. Based on the CSI parameters for the D2D channel, the eNBdetermines the appropriate transmission parameters that may include anycombination of coding, modulation, transmission power, time/frequencyresources and MIMO parameters. Other parameters may be included.

At transmission 414, the eNB 108 transmits the D2D transmissionparameters to the first UE device 102. A suitable technique includessending the parameters over the PDCCH/PDSCH.

FIG. 5 is a message diagram 500 for an example of determining a level ofinterference at the eNB 108 based on network-assigned reference signaltransmissions. The message transmission discussed with reference to FIG.5, therefore, provides an example of message transmission suitable forthe examples discussed with reference to FIG. 1A and FIG. 1C. For theexample, the third UE device 148 is a cellular UE device that is, orwill be communicating, using cellular communication. In the interest ofbrevity and clarity, some transmissions discussed with reference toother figures are not shown in FIG. 5.

At transmission 502, the eNB 108 transmits a reference signaltransmission instruction 144 to the first UE device 102 where theinstruction 144 identifies the communication resources that should beused by the first UE device 102 to transmit a first reference signal140. For the example, the instruction 144 is transmitted in thePDCCH/PDSCH although other channels can be used.

At transmission 504, the eNB 108 transmits a reference signaltransmission instruction 152 to the third UE device 148 where theinstruction identifies the communication resources that should be usedby the third UE device 148 to transmit a second reference signal 150.For the example, the instruction 152 is transmitted in the PDCCH/PDSCHalthough other channels can be used.

The first reference signal 140 is transmitted by the first UE device 102and received by the second UE device at transmission 506. The secondreference signal 150 is transmitted from the third UE device 148 at thesame time as the first reference signal 140 is transmitted from thefirst UE device 102. In the interest of clarity, FIG. 5 does not showthe two transmissions 506, 508 at the same location (frequency resource)within the message diagram. Therefore, although FIG. 5 shows thetransmission 508 below the transmission 506, the two transmissions 506,508 are occurring at the same time. The first reference signal isreceived at the second UE device and possibly received at the eNB. Thesecond reference signal 150 is received at the eNB.

As discussed above, the second UE device 104 determines the D2D channelcharacteristic information. The D2D channel characteristic informationsuch CSI parameters are reported to the eNB at transmission 510.

At event 512, the eNB determines the level of interference to the secondreference signal 150 caused by the first reference signal 140 at theeNB. Examples of suitable techniques of determining the level ofinterference include measuring total power of the first reference signalor determining power ratios of the reference signals 140, 150. Based onthe interference level, the eNB determines whether the communicationresources assigned to the first UE device for D2D communication can beassigned to the third UE device 148.

At transmission 514, the eNB 108 transmits the D2D transmissionparameters to the first UE device 102. At transmission 516, eNB 108transmits the cellular transmission parameters 516 to the third UEdevice 102 where the assigned communication resources are based on thelevel of interference. If level of interference is sufficiently low, thesame communication resources are reused and assigned to the first UEdevice and the third UE device.

FIG. 6 is a message diagram 600 for an example of determining a level ofinterference at D2D UE devices based on network-assigned referencesignal transmissions. The message transmission discussed with referenceto FIG. 6, therefore, provides an example of message transmissionsuitable for the examples discussed with reference to FIG. 1A and FIG.1D. For the example, the third UE device 148 is a D2D UE device that iscommunicating or is requesting to communicate, using D2D communication.In the interest of brevity and clarity, some transmissions discussedwith reference to other figures and they may occur in some circumstancesare not shown in FIG. 6. For example, communications with a fourth UEdevice are omitted in FIG. 6.

At transmission 602, the eNB transmits a reference signal transmissioninstruction 144 to the first UE device 102 instructing the first UEdevice to transmit a reference signal. For the example, the instructionis transmitted over the PDCCH/PDSCH channel although other channels maybe used.

At transmission 604, the eNB transmits a reference signal transmissioninstruction 158 to the third UE device 154 instructing the third UEdevice to transmit a reference signal. For the example, the instructionis transmitted over the PDCCH/PDSCH channel although other channels maybe used.

At transmission 606, the eNB transmits a reference signal receptioninstruction 146 to the second UE device 104 providing the second UEdevice 104 with information that assists the second UE device inreceiving the reference signal 140. For the example, the instruction istransmitted over the PDCCH/PDSCH channel although other channels may beused.

At transmission 608 and transmission 810, two UE devices transmit areference signal at the same time and at the same frequency. The firstUE device 102 transmits the first reference signal. The third UE device154 transmits another reference signal 156 at the same time and at thesame frequency as the first reference signal 140.

At transmission 612, the second UE device transits D2D channelcharacteristic information that includes interference informationregarding the level of interference to the first reference signal 140caused by the other reference signal 156 at the second UE device.Examples of suitable techniques of determining the level of interferenceinclude measuring total power of the first reference signal ordetermining power ratios of the reference signals.

At event 614, the eNB selects the communication resources based on thereported interference levels. Based on the interference level, the eNBdetermines whether the communication resources assigned to the first UEdevice for D2D communication can be assigned to the third UE device 148.

At transmission 616, the eNB 108 transmits the D2D transmissionparameters to the first UE device 102. At transmission 616, eNB 108transmits the D2D transmission parameters to the third UE device 102where the assigned communication resources are based on the level ofinterference. If the level of interference is sufficiently low, the samecommunication resources are reused and assigned to the first UE deviceand the third UE device.

FIG. 7 is a flowchart of an example of a method of managingcommunication using network-assisted reference signal transmissionperformed at an eNB 108. For the examples herein, the method isperformed by executing code on the controller and utilizing othercomponents of the eNB 108. The steps of the method may be performed in adifferent order and some steps may be performed simultaneously in somesituations. For example, reference signal transmission instructions canbe sent to multiple UE devices at the same time. As discussed above, thevarious examples discussed above may be performed individually orcollectively. Therefore, some steps in FIG. 7 may be omitted in somesituations. For example, in some situations, interference levels are notdetermined and step 706 is omitted.

At step 702, the eNB instructs one or more UE devices to transmit areference signal. The instructions may include messages indicating thespecific resources or may indicate a set of resources that can be usedby the devices for reference signals. In situations where the eNBexplores the possibility of reusing communication resources, thereference signal transmission instructions are sent to multiple UEdevices and specify the same time and frequency. For example, a cellularUE, one UE device from a first D2D pair and another UE device from asecond D2D pair may be instructed to transmit reference signal at thesame time and frequency. Where communication resource reuse in notcontemplated, orthogonal communication resources for reference signaltransmission are assigned to the different UE devices.

At step 704, the eNB receives reference signals transmitted from UEdevices. The eNB receives at least reference signals from cellular UEdevices to facilitate cellular uplink channel management. Where D2D UEdevices transmit reference signals, the eNB may also receive the D2D UEdevices reference signals.

At step 706, the eNB determines the level of interference at the eNB dueto D2D reference signals. Where D2D reference signals are transmitted atthe same time and frequency as cellular reference signals, the eNBdetermines the level of interference. The level of interference is usedto determine whether communication resources and be used for cellularand D2D communication for the UE devices transmitting the referencesignals.

At step 708, the eNB receives the D2D channel characteristic informationfrom the D2D UE devices receiving the D2D reference signals. In somesituations, the D2D channel characteristic information includesinterference level information. For example, where UE devices transmitreference signals at the same time and frequency, the reference signalsmay be received at other D2D UE devices and a level of interference maybe determined and reported.

At step 710, the eNB determines the D2D transmission parameters based onthe reference signals (interference level) and the D2D channelcharacteristic information. The eNB determines where communicationresources can be reused for D2D UE devices based in interference levels.The eNB also determines the appropriate transmission parameters that mayinclude any combination of coding, modulation, transmission power,time/frequency resources and MIMO parameters. Other parameters may beincluded.

At step 712, the D2D transmission parameters are assigned to the D2D UEdevices. The parameters may be assigned using PDCCH/PDSCH.

FIG. 8 is an illustration of an example of a transmission by a D2D UEdevice including reference signals. The eNB configures the D2D UE deviceto transmit a reference signal 140. The transmission in the cellularuplink communication band in accordance with one or more revisions ofthe 3GPP LTE specification, although the cellular downlink band may beused in some situations. For the example of FIG. 8, the eNB configuresthe D2D UE device to transmit the reference signal in fixed frequencybands used for D2D transmission. Where multiple D2D UE devices areconfigured and interference is not determined, the eNB configures theD2D UE devices to transmit reference signal on orthogonal resources.

For the example, the reference signal 140 transmitted at a period of Tsubframes 802. After transmitting the reference signal, the UE devicereceives the D2D transmission parameters from the eNB and transmits ascheduling assignment 804 in subframe n 806. The scheduling assignment(SA) 804 indicates the D2D communication resources that will be used forD2D transmission in subsequent subframes. For the example, the SA 804identifies D2D communication resources in four subframes 808, 812, 814,816 that should be used for D2D transmissions. In the subframe n+x808,the UE device transmits a D2D transmission 810. The UE devices alsotransmits data in the subframe n+x+1 812, the subframe n+y 814 and thesubframe n+y+1 816.

Clearly, other embodiments and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. The above description is illustrative and not restrictive.This invention is to be limited only by the following claims, whichinclude all such embodiments and modifications when viewed inconjunction with the above specification and accompanying drawings. Thescope of the invention should, therefore, be determined not withreference to the above description, but instead should be determinedwith reference to the appended claims along with their full scope ofequivalents.

The invention claimed is:
 1. A method comprising: receiving firstinformation from a base station, at a first user equipment (UE) device,to transmit a reference signal, the first information identifying afirst configuration for sending the reference signal to a second UEdevice; receiving second information not transmitted in the referencesignal, at the second UE device, the second information identifying asecond configuration for receiving the reference signal from the firstUE device; determining, at the second UE device, device-to-device (D2D)channel characteristic information by measuring at least one signalparameter of a UE device received reference signal that is the referencesignal transmitted by the first UE device as received at the second UEdevice, the D2D channel characteristic information indicative of a D2Dcommunication link between the first UE device and the second UE device,the first information not transmitted in the reference signal; andtransmitting the D2D channel characteristic information from the secondUE device in response to receiving the second information anddetermining the D2D channel characteristic information, wherein the D2Dchannel characteristic information is based on a plurality of UE devicereceived reference signals received at the second UE device at differenttimes.
 2. The method of claim 1, wherein the determining the D2D channelcharacteristic information comprises determining the D2D channelcharacteristic information based on a plurality of messages transmittedfrom the second UE device at different times.
 3. The method of claim 1,further comprising: transmitting, to the second UE device, referencesignal information at least partially characterizing the referencesignal.
 4. The method of claim 1, wherein the first information receivedat the first UE device comprises resource information identifying a setof communication resources allocated for transmission of the referencesignal, the reference signal transmitted using selected communicationresources selected by the first UE device.
 5. The method of claim 4,further comprising: transmitting, to the second UE device, referencesignal information at least partially characterizing the referencesignal wherein the reference signal information includes at least one ofa UE identification code assigned to the first UE device, hoppingpattern used for reference signal transmission by the first UE device, areference signal code, and the set of communication resources.
 6. Themethod of claim 1, further comprising: receiving an instruction, at athird UE device to transmit another reference signal at the same timeand using communication resources assigned to the first UE device fortransmitting the reference signal; transmitting, from the third UEdevice to the second UE device, the reference signal in response to theinstruction; determining a level of interference between the anotherreference signal and the reference signal transmitted by the first UEdevice; and allocating, based on the level of interference,communication resources to the first UE device and to the third UEdevice.
 7. The method of claim 6, wherein the same communicationresources are allocated to the first UE device and the third UE devicewhen the level of interference is below a threshold.
 8. The method ofclaim 7, wherein the allocating comprises allocating D2D communicationresources to the first UE device for D2D communication and allocatingcellular communication resources to the third UE device for cellularcommunication.
 9. The method of claim 7, wherein the allocatingcomprises allocating D2D communication resources to the first UE devicefor D2D communication and to the third UE device for D2D communication.10. The method of claim 1, wherein the measuring the at least one signalparameter of the UE device received reference signal comprises measuringat least one signal parameter that indicates a quality of the D2Dcommunication link.
 11. The method of claim 1, wherein the measuring theat least one signal parameter of the UE device received reference signalcomprises measuring at least one signal parameter that indicates arequired transmission power for successful reception over the D2Dcommunication link.
 12. The method of claim 1, wherein the measuring theat least one signal parameter of the UE device received reference signalcomprises measuring at least one signal parameter that indicates a powerlevel related to the UE device received reference signal.
 13. The methodof claim 12, wherein the power level is a total received power of the UEdevice received reference signal.
 14. The method of claim 12, whereinthe power level is a signal to-noise-ratio (SNR).
 15. The method ofclaim 12, wherein the power level is a signal-to-interference-plus-noiseratio (SINR).
 16. The method of claim 1, wherein the first informationis sent over System Information Block (SIB) broadcasted from the basestation.
 17. The method of claim 1, wherein the first information issent over higher layer signaling from the base station.
 18. A methodcomprising: receiving, from a base station at a first user equipment(UE) device, first reference signal transmission information, the firstreference signal transmission information identifying a firstconfiguration for sending a reference signal to a second UE device;transmitting, from the first UE device to a second UE device, areference signal in accordance with the reference signal transmissioninformation and within a device-to-device (D2D) data communicationchannel between the first UE device and the second UE device, thereference signal transmission information not transmitted in thereference signal; receiving second reference signal transmissioninformation not transmitted in the reference signal, at the second UEdevice, the second reference signal transmission information identifyinga second configuration for receiving the reference signal from the firstUE device; determining, at the second UE device, channel characteristicinformation indicative of a D2D communication link between the first UEdevice and the second UE device, the D2D channel characteristicinformation determined by measuring at least one signal parameter of aUE device received reference signal that is the reference signaltransmitted by the first UE device as received at the second UE device,the reference signal transmitted in accordance with the first referencesignal transmission information and within a device-to-device (D2D) datacommunication channel between the first UE device and the second UEdevice, the first reference signal transmission information nottransmitted in the reference signal; and transmitting the D2D channelcharacteristic information from the second UE device; and performing theD2D communication between the first UE device and the second UE devicebased on the D2D channel characteristic information, wherein the D2Dchannel characteristic information is based on a plurality of UE devicereceived reference signals received at the second UE device at differenttimes.
 19. The method of claim 18, wherein the transmitting thereference signal comprises transmitting the reference signal istransmitted within at least one subframe of a frame comprising aplurality of subframes where at least one other subframe includes D2Ddata.
 20. The method of claim 19, wherein each subframe of the pluralityof subframes is divided in time and frequency such that each subframecomprises a plurality of time/frequency communication resources andwherein transmitting the reference signal comprises transmitting thereference signal is transmitted within at least one time/frequencycommunication resource of the at least one subframe.
 21. The method ofclaim 18, further comprising: performing the D2D communication betweenthe first UE device and the second UE device, wherein performing the D2Dcommunication between the first UE device and the second UE devicecomprises communicating within at least one time/frequency communicationresource of the D2D data communication channel, the at least onetime/frequency communication resource determined based on the D2Dchannel characteristic information.
 22. The method of claim 21, whereinthe D2D channel characteristic information comprises channel stateinformation (CSI).
 23. The method of claim 21, wherein the at least onetime/frequency communication resource is within one of a plurality ofsubframes of a frame, the reference signal transmitted within at leastone other subframe of the frame.
 24. The method of claim 21, furthercomprising: determining, at the base station, the at least onetime/frequency communication resource based on the D2D channelcharacteristic information.
 25. A first user equipment (UE) devicecomprising: a receiver configured to: receive, from a second UE device,a reference signal, the second UE device transmitting the referencesignal in response to receiving first information from a base station,the first information identifying a first configuration for sending thereference signal to the first UE device, and receive second informationnot transmitted in the reference signal, the second informationidentifying a second configuration for receiving the reference signalfrom the second UE device; a controller configured to determinedevice-to-device (D2D) channel characteristic information by measuringat least one signal parameter of a UE device received reference signalthat is the reference signal transmitted by the second UE device asreceived at the first UE device, the D2D channel characteristicinformation indicative of a D2D communication link between the first UEdevice and the second UE device, the first information not transmittedin the reference signal; and a transmitter configured to transmit theD2D channel characteristic information in response to receiving thesecond information and determining the D2D channel characteristicinformation, wherein the controller is configured to determine D2Dchannel characteristic information based on a plurality of UE devicereceived reference signals received at the first UE device at differenttimes.
 26. The UE device of claim 25, wherein the receiver is configuredto receive, from the second UE device, reference signal information atleast partially characterizing the reference signal.
 27. The UE deviceof claim 25, wherein the receiver is further configured to receive, fromthe second UE device, reference signal information at least partiallycharacterizing the reference signal, the reference signal informationincluding at least one of a UE identification code assigned to thesecond UE device, hopping pattern used for reference signal transmissionby the second UE device, a reference signal code, and the set ofcommunication resources.